1. Field of Invention
This invention pertains to a method and an apparatus for shaping an elongated hollow or solid article, and more particularly to a method and apparatus for performing consistent, accurate spatial dimensional shaping of an elongated extruded product.
2. Description of the Art
There are a considerable number of operating parameters and conditions present in various metal forming methods which cause finished products to exhibit dimensional variability. In certain processes the dimensional variability is acceptable, while in other processes the dimensional variability is unacceptable and requires subsequent metal finishing operations.
In the extrusion process, for example, a heated ingot or billet is forced to flow under pressure through a die opening to form an elongated article such as a channel, a tube or an angle. In a typical aluminum extrusion process the extruded product is forced through the die at forces in the 500 to 15,000 ton range. The extrusion exits the die of an extrusion press at elevated temperatures on the order of 300.degree. to 1200.degree. F. It is common to solution heat treat and quench the extruded product in an in-line solution heat treating process or by a separate solution heat treatment process. Such extruded product may be made to various lengths, including lengths in excess of 150 feet, and may be of diverse cross-sectional configuration.
Considering the operating parameters of the extrusion process including pressures, temperatures, die condition and product length, and considering the effects of subsequent heat treatment and quenching, it is understandable that extruded metal products may exhibit considerable dimensional variation about the cross-section and over the length of the product. It is also understandable that such dimensional variation may be present from product cycle to product cycle and from extrusion run to extrusion run. It is therefore often necessary to perform subsequent metal finishing operations to bring the product within acceptable dimensional tolerance. There are some dimensional variations on extruded metal products which are not readily correctable by conventional metal finishing operations, including bending, roll straightening and hammering. In such conventional metal finishing operations, springback is a major concern. Such springback may be so extreme, especially in products with substantial dimensional variation, that such conventional metal finishing operations are inadequate.
Prior shaping methods and apparatus have provided methods to finish the shape of articles, such as extrusions. The tolerances currently permissible for such products, as published by the Aluminum Association, particularly for thin walled extrusions, are so broad that the products may be precluded from certain critical applications. If the dimensional deviation could be reduced, the products may be applicable in an increased number of applications where dimension is important. Furthermore, the dimensional quality of the product in existing applications could be dramatically increased.
Despite prior art attempts to improve the dimensional tolerance and minimize dimensional variation in a finishing operation, there is a need for further improvement. Accordingly, a stretch shaping method and apparatus are desired which results in finish shaping an elongated article, such as an extrusion, to minimize cross-sectional and longitudinal dimensional deviations from nominal value.